The phenomenon that ferromagnetic and ferrimagnetic materials undergo a small change in length and volume due to change in the magnetization state is referred to as magnetostriction, in which the change in volume is mentioned as “volume magnetostriction”, and the change in length is called as “linear magnetostriction”. Practical magnetostrictive materials refer to those having the linear magnetostrictive property. The degree of magnetostriction is presented by magnetostriction coefficient λ, λ=ΔL/L (L refers to the initial length of the material, ΔL refers to the change in length when the magnetization state is changed). The maximum magnetostriction coefficient, when the material is magnetized, is called saturated magnetostriction coefficient λs. Generally, (3/2)λs is used as the parameter for characterizing the property of magnetostriction of a material. The value of (3/2)λs can be calculated by applying the expressions (3/2)λs=λ//−λ⊥, in which λ// refers to the saturated magnetostriction coefficient measured along the direction parallel to the direction of the magnetic field, and λ⊥ refers to the saturated magnetostriction coefficient measured along the direction perpendicular to the direction of the magnetic field.
As one kind of energy-transducing materials, the magnetostrictive material began to be applied to the technical field of energy transduction from 40s to 50s of the twentieth century, since the magnetostrictive materials could generate great force with a short response time when the materials undergo the magnetostriction. Later, the magnetostrictive materials were also applied to the fields of actuators, sensors and so on. Researchers focus their attentions onto improvement in the magnetostriction coefficient of the materials and onto development of novel materials with high magnetostriction coefficient, since the degree of energy-transduction of the magnetostrictive material is proportioned to the square of the magnetostriction coefficient, in the case that the magnetostrictive material is used as an energy-transducing material.
Traditional magnetostrictive material may be made of pure Ni, Ni-based alloy, Fe-based alloy and ferrite. A polycrystalline pure Ni has magnetostriction coefficient of 35 ppm to 40 ppm (1 ppm=10−6), the magnetostriction coefficients of practical Ni-based alloy and Fe-based alloy are lower than 100 ppm, and the magnetostriction coefficients of ferrite is usually in between 10 ppm to 50 ppm.
Clark et al. of US provided a magnetostrictive material containing a rare earth metal and Fe as main components, which is referred to as rare earth giant magnetostrictive material. The rare earth giant magnetostrictive material has very high magnetostriction coefficient. A single crystal rare earth giant magnetostrictive material may have a magnetostriction coefficient of up to 2000 ppm. The magnetostriction coefficient of a polycrystalline rare earth giant magnetostrictive material may reach up to 1000 to 1500 ppm under a magnetic field of 80 kA/m and a certain pre-pressure stress. The polycrystalline rare earth giant magnetostrictive material is well applied in a field of underwater sound transducer as it has high strain and low Young modulus. However, the main phase of the polycrystalline rare earth giant magnetostrictive material is Laves phase intermetallic compound, which has intrinsic embrittlement and bad environmental tolerance, and thereby limits its applicability in various fields. In addition, this kind of material has high electrical conductivity, which seriously deteriorates the energy output or the shift output thereof due to eddy current loss when it is used under a higher frequency.
In the year of 2000, S. Guruswamy et al. (USA) reported a binary alloy which consisted of Fe and Ga (S. Guruswamy, et al. Strong, dutile, and low-field-magnetostrictive alloys based on Fe—Ga. Scripta Mater. 2000, 43: p 239-244), i.e. Fe—Ga alloy. Fe—Ga alloy is a novel magnetostrictive material having a λ value of at least one time higher than that of traditional magnetostrictive materials and much higher intensity and magnetic permeability than that of the giant magnetostrictive materials.
The magnetostriction coefficient of Fe—Ga alloy is lower than that of the giant magnetostrictive materials, but much higher than that of the traditional magnetostrictive materials. Moreover, Fe—Ga alloy overcomes the defects of the giant magnetostrictive materials in regard to their intensity, magnetic permeability and so on. Therefore, Fe—Ga alloy has good application prospects in making transducers, actuators, sensors, and so on. However, the alloy may have eddy current loss when being used under a high frequency due to its quite low resistivity.
Accordingly, people have been trying to make the Fe—Ga alloy into thin-sheet form, so as to lower the eddy current loss in working status.
In the year of 2003, R. A. Kellogg et al. (USA) obtained a thin-sheet material having a saturated magnetostriction coefficient (3/2)λs of about 170 ppm by subjecting the alloy Fe83Ga17 to treatments of hot rolling, warm rolling, and those heat-treatments for its recovery and re-crystallization (R. A. Kellogg, A. B. Flatau, et al., Texture and grain morphology dependencies of saturated magnetostriction in rolled polycrystalline Fe83Ga17; J. Applied Physics. 2003, Vol. 93, No. 10: p 8495-8497).
In 2004, N. Srisukhumbowornchai et al. (USA) reported that a Fe—Ga-based thin-sheet material with a magnetostrictive property was obtained by hot rolling, twice warm rolling at 400° C. and subsequent heat treatments of the Fe85Ga15 alloy in which 1 mol pct of NbC was added (N. Srisukhumbowornchai, S. Guruswamy, Crystallographic textures in rolled and annealed Fe—Ga and Fe—Al alloys. Metallurgical and Materials Transactions A. 2004, Vol. 35A: p 2963-2970).
In 2005, Suok-Min Na and Alison B. Flatau et al. (USA) reported that a thin-sheet material with magnetostriction property was obtained by hot rolling, warm rolling and vulcanization (surface-energy-induced texture) of the Fe81.3Ga18.7 alloy in which 0.5 at. % B was added (Suok-Min Na, Alison B. Flatau. Magnetostriction and surface-energy-induced selective grain growth in rolled Galfenol doped with sulfur. Proceedings of SPIE. 2005, Vol. 5761: p 192-199). The magnetostriction coefficient (3/2)λs of the thin-sheet material obtained by this method is up to about 220 ppm (Suok-Min Na, Alison B. Flatau. Magnetostricton and crystallographic texture in rolled and annealed Fe—Ga based alloys. Mater. Res. Soc. Symp. Proc. Vol. 888, V06-10, 2006 Materials Research Society, p 335-340).
In 2006, Mungsantisuk et al. (USA) obtained a Fe—Ga-based magnetostrictive thin-sheet material by hot rolling, twice warm rolling at 400° C. and subsequent heat treatments of Fe—Ga-based alloy in which NbC or Be or Al or combinations thereof is added, wherein the alloy is sheathed to prevent oxidization and heat loss from the alloy surface during rolling (WO 2006/094251 A2).
The common deficiencies of said Fe—Ga-based magnetostrictive thin-sheet materials is that these alloy materials have bad ductibility and anti-oxidization; and their manufacturing processes are excessively complicated, including unavoidable warm rolling over more than 100 passes in total between the steps of hot rolling and cold rolling, repeatedly stress-relief annealing during rolling, and sometimes sheathing the master alloy.